1. Field of the Invention
This invention relates to a dark privacy glass having a low solar factor, and more particularly, to vehicle windows, e.g. automotive roof windows made using the dark privacy glass, the windows having a solar factor equal to or below 30% calculated in accordance to the International Organization for Standardization (“ISO”) No.13837.
2. Discussion of the Technical Challenge
There is continued interest in reducing the load applied to vehicle engines, e.g. automotive gasoline engines to increase the miles per gallon of gasoline and to reduce the carbon monoxide exhausted from the engines. Of particular interest in the present discussion are the imposed and the proposed regulations of the Federal Clean Air Act and of the California Air Resources Board (“CARB”) directed to vehicle windows, e.g. automotive windows to reduce solar energy passing through the windows to reduce solar heating of the vehicle interior. As is appreciated by those skilled in the art, reducing solar heating of the vehicle interior, especially during the summer months reduces the air conditioner load on the engine. The proposed CARB regulation includes regulations directed to the automotive roof window and requires that the transparency of the roof window, e.g. the glass transparency have a solar factor of a specified value determined according to International Organization for Standardization (“ISO”) No,13837. As is appreciated by those skilled in the art, the automotive roof window can be securely mounted in the roof or can be mounted in the roof for reciprocating movement between an open position and a closed position. Further automotive roof windows are also referred to as sun windows and moon windows.
The solar factor is a measure of the percent of solar energy or heat that passes through the glass transparency, e.g. the roof window into the car interior. The lower the solar factor, the higher the solar protection and the higher the performance of the glass transparency in preventing passage of solar energy into the vehicle interior. Using a solar control glass transparency can reduce the need for air-conditioning, thereby reducing air pollution and increasing miles per gallon of fuel.
The formula for calculating the solar factor recited in ISO No. 13837 includes the following variables: total solar energy transmission of the transparency; total solar energy reflectance of the transparency; total solar energy absorbance of the transparency, emissivity of the surfaces of the transparency facing the interior and exterior of the vehicle, speed of the wind moving over the exterior surface of the transparency, thickness of the transparency and heat transfer coefficient of the interior and the exterior surfaces of the transparency. A government, state or municipal agency selects the value of the solar factor. By way of illustration and of interest to the present discussion, CARB has selected a solar factor for transparencies for roof windows of equal to or less than 30%.
As can be appreciated by those skilled in the art, it would be commercially advantageous to provide glass transparencies for vehicle roof windows that meet the solar factor requirement set by the government, state and/or municipal agencies, e.g. but not limiting to the solar factor set by CARB.